Jet fuels or diesel fuels that are clean and contain substantially no sulfur, nitrogen, or aromatics are expected to be on the verge of a dramatic increase in demand, for example to meet the pressing need of automobile manufacturers for a global standard. See the testimony to the U.S. Congress of Oct. 5, 1999 by James A. Spearot, Director, Chemical and Environmental Sciences Laboratory, General Motors, on behalf of the Partnership for a New Generation of Vehicles Advanced Fuels Group. However there are substantial unsolved technical problems connected with such a development.
Certain quite recently developed fuel compositions are clean, but are seriously deficient in certain fuel-desirable technical attributes. These are, apparently, lost along with the removal of sulfur and/or nitrogen. Accordingly there is a newly emergent need, and corresponding thereto, a significant technical problem to be solved. This is: how to secure improved clean jet or diesel fuel which more effectively compensates for removal of sulfur and/or nitrogen and/or aromatics, especially for removal of sulfur.
Such novel fuels would comply with increasingly stringent regulatory standards, and would be highly sought after by the consumer both for their improved environmental acceptability, and for their lack of compromise in terms of effectiveness, especially for fuel system lubrication of injectors and fuel pumps, in modern engines.
Another growing need in the field of low sulfur jet/diesel fuels (including in general sulfur-free types) is the need for a common or “fungible”, i.e., economically interchangeable, fuel/additive or fuel additive “concentrate”. Such commonality would permit a relatively small number of specialized plants, such as Fischer-Tropsch plants, to serve as a source of supply of a “concentrate” which could be blended in any petroleum refinery with all manner of jet/diesel fuels, especially low-sulfur fuels, including hydrodesulfurized and/or biodesulfurized conventional petroleum fuels as well as Fischer-Tropsch derived fuels. Thus the benefit of the additive would be spread over all the principal ultra-low sulfur jet/diesel fuels, and solve for all of them the problems incurred by sulfur-removal. Such a benefit could indeed be material to the protection of the entire base of investment in conventional petroleum refining. Moreover, if the additive were to be a concentrate, the above need would be addressed much more viably and economically.
Unfortunately, known processes for making fuel lubricating additives of the relatively long-chain type required are subject to intrinsically producing too low a level of useful additive, diluted by hydrocarbons which are uneconomical to transport or to remove. Moreover, there is significant room for improvement in the properties of such additives.
Known processes for example include those which produce so called “native” alcohols in a Fischer-Tropsch derived fuel; such processes currently are lacking in having both an inadequate type and level of branching in the native alcohol. Moreover, the total amount of such “native” alcohols is insufficient when blending to high dilution for modern jet/diesel fuel lubrication. Further, in products of such processes, there is no independent variability of branching/heavy atom count in the alcohol as compared to the copresent fuel hydrocarbons, thus no possibility of concurrently optimizing (a) lubricity properties and (b) other important parameters, e.g., cetane number or smoke point. (Heavy atom count for hydrocarbon=sum of carbon atoms; heavy atom count for alcohol=sum of carbon and oxygen atoms).
Non-alcohol approaches to additives for low sulfur fuels have been tried and found wanting. State of the art, for example, is represented by WO 96/25473; WO 98/21293; WO 98/28383; WO 99/00467; and U.S. Pat. No. 5,488,191. Such additives have one or more important disadvantages, for example they contain nitrogen, aromatic rings, have overly high molecular weight, or are relatively uneconomical.
Particularly desirable, then, would be a common, concentrated, biodegradable, economical additive which is more lubricious. Ideally, such an additive would be less polar, and dramatically lower melting than any known additive currently available on commercial scale in concentrate form. Moreover, such a particularly desirable additive would be free from disadvantages such as excessively high molecular weight, and would completely and cleanly combust without any difficulty. Compositions comprising such an additive would permit independent control of the structure of the alcohols and the structure of the fuel hydrocarbons, for an overall optimization of the fuel properties of mixtures containing both.
Accordingly, it is an object of the present invention to secure such a concentrated additive, derivative low-sulfur- or zero-sulfur-fuels containing it, and processes for making it.
Processes for making jet and/or diesel fuels have been markedly improved in recent years. Such processes include deep hydroprocessing of crudes as well as recently improved Fischer-Tropsch slurry bed reactions to convert synthesis gas (syngas) to a wax, followed by hydrocracking/hydroisomerization and distillation to separate the desired fuel streams. The products can be optimized around jet/diesel.
The present invention substantially modifies such processes and compositions, affords novel fuel compositions, including the desired concentrated additive, and solves the aforementioned technical problems.
Compositions of the present invention have numerous advantages, for example in permitting a much greater flexibility for the formulator in producing finished fuels, or concentrated additive blendstocks which are clean, highly biodegradable, have superior lubrication properties, and can be pipelined or shipped as liquids under ambient or even arctic temperatures (e.g., −30 deg. F. or even lower).
The inventive fuels and processes permit independent optimization of the properties of fuel hydrocarbons and alcohols for overall superior results.
An especially important advantage is that the concentrated additives or “concentrates” of the invention separate much less readily from diluted blendstocks and/or finished fuels at low temperatures. This makes them highly desirable in a number of critical applications, including for use in jet fuel. Further, in preferred embodiments, the compositions are substantially olefin—free and carboxylate—free, thereby essentially eliminating peroxide forming tendencies and reducing corrosion/gum formation.
The present invention is accompanied by advantages useful not only to the manufacturers and consumers of fuels, but also to manufacturers and consumers of detergents, for example in that, by promoting the manufacture of selected alcohols for fuel uses, important economies of scale will make similar alcohols much more affordable for detergent uses.